What about a used D40 or D3000 and the 50mm or 18-55mm VR would be under £300 easily - however you're unlikely to get one that can shoot HD video for £300
http://www.mpbphotographic.co.uk/use...nikon-d3000-2/
http://www.mpbphotographic.co.uk/use...x-11111111221/
Marcus